Process for facilitating the plastic deformation of metals



United States Patent C) Fritz Singer, Starnberg, Germany ApplicationNovember 19, 1957 Serial No. 697,335

11 Claims. (Cl. 148-624) No Drawing.

This invention relates to a process for facilitating the plasticdeformation of metals, and particularly to a process for producing acoating on metals of the ferrous group, which coating serves tofacilitate such deformation.

This application is a continuation in part of my co pending patentapplication, Serial No. 548,267, filed November 21, 1955, now abandoned,which is a continuation in part of my patent application, Serial No.256,134. filed November 13, 1951, now abandoned.

In my United States Patent No. 2,105,015, I have described a process forfacilitating the plastic deformation of iron or steel by forming aphosphate or other crystalline coating on the article to be deformed.This process is now extensively used for facilitatnig the cold drawingof wire and tubes and the cold extrusion of hollow steel casings.

Subsequent to my above patent it was discovered that sulfide coatingsfurnish advantages over phosphate coatings in their capacity forfacilitating plastic deformation While the phosphate coatings are of thecoated metal. of crystalline and brittle nature and serve primarily as ameans for preventing contact between the surfaces of work pieces andtools, and as carriers for lubricants, the sulfide coatings areamorphous, soft and plastic, and are capable of acting not only as aseparating layer, but also they themselves serve as a very eflicientlubricant.

Various methods have previously been proposed for producing sulfidecoatings, particularly on ferrous surfaces. According to one of thesemethods, the ferrous articles are immersed in water through whichhydrogen sulfide is bubbled, or they are first wetted with water andthen subjected to hydrogen sulfide gas. The thus produced sulfidecoating is dark and is not firmly bonded to the surface. Anotherdrawback of this process consists in the formation of aqueous solutionsof poisonous hydrogen sulfide, requiring measures for protecting theworkers from poisonous gases when the articles are introduced in andtaken out of the bath.

While the sulfide coating which is not firmly bonded facilitates coldworking to some degree, it is far less effective than my hereindescribed sulfide coating which is firmly bonded to the surface.

Referring again to the prior art, it has been proposed to produce asulfide coating in the cold working operation itself by using so-calledsulfidizing lubricants of water-soluble sulfides such as ammoniumsulfide or ammonium polysulfide added to oil-in-water emulsions. Suchsulfidizing lubricants may be effective but the r use is limited to thecold working of low-carbon steels or non-ferrous metals. Anotherdrawback of sulfidizing lubricants of this kind is their offensive odor.

With the foregoing in mind, it is an object. of the present invention toprovide a new and improved process for facilitating the plasticdeformation of a metal, which does not suffer the prior disadvantages.

Another object is to provide a new and improved process for facilitatingthe plastic deformation of a metal "ice wherein a tightly adherent metalsulfide coating is pro duced on the metal.

A further object is to provide a process for facilitating the plasticdeformation or working of ferrous metals which is simple and reliable inuse and productive of improved coatings.

An additional object is to provide an economical and practical processwhich may be used on high carbon, alloy and other types of hard ferrousmetal. These and other objects and advantages of the invention willbecome apparent upon reading the following specification.

In accordance with my invention, the plastic deformation of metals ofthe ferrous group is facilitated by producing a tightly adherent sulfidecoating thereon. The plastic deformation is carried out shortly aftercoating the metal, or the operation may take place subsequently if thecoating is protected against oxidation in the meantime. The process isespecially useful in cold working metals of the ferrous group such asiron, nickel and cobalt.

According to a preferred embodiment of my invention, the metal in thedry state is exposed to the action of a hydrogen sulfide and oxygen ineffective amounts throughout the formation of the coating. The hydrogensulfide and the oxygen are preferably supplied in stoichiometric amountsduring the formation of the coating to carry out the reaction accordingto the equation,

where R is iron, nickel or cobalt. Excesses, to drive the reaction andto provide for losses due to oxidation-reduction side reactions, aretolerable to a small degree but should be reduced as much as possible.

When a hydrogen sulfide is referred to herein, it is intended to includeboth hydrogen sulfide and hydrogen polysulfides. The hydrogen sulfidemay be supplied as free or chemically uncombined hydrogen sulfide, or itmay be supplied by a hydrogen sulfide-producing substance. It may beemployed in the gaseous state, as free H S, or as a product of thedissociation or decomposition of a substance to H 8. The hydrogensulfide may also be produced or liberated directly on the surface of themetal, as by decomposition of a hydrogen sulfide-producing chemicalcomposition.

Reference to oxygen contemplates free or chemically uncombined oxygen.Air is the preferred oxygen-containing gas for the reaction. Air ofnormal humidity will serve to supply the oxygen and the small watervapor requirements. The gaseous source of hydrogen sulfide may containwater vapor, as is usually the case when H 5 is produced by wet methods.Moisture present on the surface of the metal may also contribute to thereaction. The humidity of the atmosphere surrounding the metal beingtreated Will vary under different conditions. It is ordinarily preferredthat the atmosphere have a relative humidity of about 30-70% for easeand rapidity of reaction. Higher humidities are preferably avoided toavoid oxidation of the sulfide coatings and to avoid the loose formationof the sulfide coatings. Water vapor is a product of the reaction and isnot consumed but performs a function catalytic in nature, so that theexact quantity of water vapor present is not of great importance.

In referring to the dry state of the metal I mean that the metal surfaceneed only, be visibly dryor visibly free of water or other liquid,although it may contain dispersed, adsorbed or occluded moisture. .Wateror. other liquid must preferably not be present on the metal surface inthe continuous state 'or phase, that is, as, a flowable liquid or aliquid film. This condition is mandatory for producing a tightlyadherent protective coating according to the invention. Thus,'oxygenrnust' 3 be presentin effective amounts or concentrations at thereacting metal surface throughout the production of the coating, andthis condition is only achieved when the metalis in the dry state andfree from layers of liquid on the surface.

When proceeding according to my invention, the metal surface is exposedto the simultaneous presence and reaetionof hydrogen sulfide and oxygensupplied in stoichiometric quantities. The reaction and formation of thecoating on ferrous surfaces takes place in the presence of water vaporaccording to the simplified equation:

While the invention is not limited to theoretical considerations, apostulated course of the reaction is as follows. Hydrogen sulfide in thepresence of oxygen and water vapor is gradually oxidized to sulfur. Thereaction is not simple but takes a complicated course with the formationof unstable intermediate products. It is further postulatedthat theformation of the metal sulfide coating is not caused by the directaction of the hydrogen sulfide, but by the intermediate products of theoxidation of the hydrogen sulfide. For this reaction to take place andproduce a tightly adherent iron sulfide coating, it is necessary thatthe metal surface be free of liquid water.

Where liquid water is present on the metal surface as in prior artprocesses, it is an aqueous solution of hydrogen sulfide which reacts.Although hydrogen sultide is a very weak acid, an aqeous solutionthereof reacts with ferrous surfaces very rapidly. This reactionproceeds according to the following equation:

The hydrogen liberated in the rapid reaction with the aqueous solutionseemingly separates the iron sulfide produced from the metal surface andthus produces a loosely adherent coating. Even the presence of air doesnot alter the course of the reaction. Hyrogen sulfide is readily solublein water (1 volume part of water dissolves 2.61 volume parts of H 8 at20 C.), while the solubility of oxygen is low (1 part of water dissolves0.031 part of oxygen at 20 C.). Thus, any oxygen dissolved in theaqueous solution of hydrogen sulfide does not reach the reaction zone,namely, the ferrous surface, as it is rapidly consumed in anoxidation-reduction reaction with the hydrogen sulfide. The result ofthe prior art treatment of the metal surface with hydrogen sulfide inthe presence of liquid water appears to be a rapid reaction, requiringperhaps only seconds, which produces a loosely .bound coating.

In my invention, involving a different type of reaction, a firmly bondedsulfide coating may be produced in about to 60 minutes. The differencein magnitude of the reaction time may be caused in part by therelatively low concentration of hydrogen sulfide in the reaction zoneand its gradual supply to the reaction surface and consumption thereon.The slow formation of the sulfide coating contributes, however, to thefirm bonding of the coating. The process can be controlled so that thehydrogen sulfide is completely consumed and there are no difiicultiescaused by noxious gases when the coated articles are removed from thereaction chamber. This is accomplished by supplying approximatelystoichiometric quantities of hydrogen sulfide and oxygen during thereaction.

According to one method of carrying out my invention, the metal iscontacted With hydrogen sulfide in the gaseous state. According to thisembodiment, it will be necessary first to remove any scale from themetal. The metal de-scaled and in a visibly dry state may be placed in aclosed chamber, which can be a wooden box, into which hydrogen sulfideis introduced. Instead 93 8 a i dies? alfi erodu ss substance may edisli ed a hu o nlfide .t rHS),

which volatilizes at normal temperatures and dissociates into ammoniaand hydrogen sulfide. The metal to be coated will often come directlyfrom a pickling operation where scale has been removed, and it need notbe absolutely dry but may be placed in the reaction chamber as soon asany visible water has disappeared. The moisture adsorbed or occluded onthe metal surface and which is not visible is useful in initiating theprocess.

Where the total surface area of the metal in the chamber is not toogreat, the air originally present properly diluted with hydrogen sulfidemay supply enough oxygen for the formation of the coating. Otherwise,the supply of hydrogen sulfide can be supplemented by the introductionof air or other oxygen-containing gas from time to time or continuously,to replace the oxygen consumed in the formation of the coating and byoxidation of hydrogen sulfide, so that approximately stoichiometricproportions are present throughout the coating operation. It is normallyunnecessary to introduce water vapor specifically, as noted above, sincethe average relative humidity of air is sutficient and water vapor isformed in the reaction. There may also be water vapor present in thehydrogen sulfide.

To conserve hydrogen sulfide and to avoid giving off noxious gas, it isadvisable to compute approximately the linear surface of the charge tobe coated. This latter computation helps to determine the stoichiometricquantities. The amount of hydrogen sulfide supplied will depend upon thethickness of the coating which is desired. The coating will generally beformed in about 20 to 60 minutes, depending upon the desired thicknessof the coating. When combined hydrogen sulfide is used, the resultingcoating has a bright irridescent appearance, and its color variesbetween silver and brass. When ammonium hydrosulfide is volatilized, thecoating is generally black with no metallic luster.

In carrying out the coating operation, approximately stoichiometricproportions of hydrogen sulfide and oxygen are supplied in the presenceof water vapor to effect the desired coating. However it should beunderstood that there may occur some deviation in the stoichiometricproportions without endangering the formation of the coating. Thesulfide coating produced is resistant to the action of a surplus ofoxygen and in case of a surplus of hydrogen sulfide the reaction wouldmerely stop. In practice the operator will preferably interrupt thesupply of humid air upon a change in the color of the coating from blackto brown. To this extent, the proportions of the reacting ingredientsare critical to prevent oxidation of the sulfide coating.

Another very efficient and simple method of treating the articles withhydrogen sulfide according to my invention consists in dipping orspraying the articles with an aqueous solution of ammonium sulfide orammonium polysulfide, allowing them to drain and dry and then subjectingthem to air until a black coating is formed. The formation of thetightly adherent sulfide coating is effected by the combined action ofthe dissociating ammonium hydrosulfide or the polysulfide and the oxygenof the air after the ammonium sulfide solution has dried. In order toretain the necessary quantities of ammonium sulfide on the iron surface,it may be necessary to increase the very low viscosity of the ammoniumsulfide solutions by adding thickening agents such as methylcellulose orcellulose glycolate. To produce a sulfide coating on ordinary steel, thearticles may be dipped into a 20% aqueous solution of ammoniumhydrosulfide into which .5 to 1% methyl-cellulose or cellulose glycolatehas been stirred. The articles are allowed to drain and dry and are thensubjected to air of normal humidity at normal or slightly elevatedtemperatures, for example 30 to 50 Centigrade. When using yellowammonium poly sulfide or ammonium sulfide. containing ammoniumpolysulfide, t e s l t n. upon be gme paq e .d e to t e s n rati s ofolloida su fur.

Because the sulfide coatings are liable to be oxidized in the humidatmosphere, the ferrous articles after being coated are preferablyeither immediately cold worked or are stored in a dry atmosphere.

Important fields of application of the invention are cold drawing andcold extrusion of ferrous metals, especially in wire, profile and tubedrawing. The new process is especially useful in facilitating thedeformation of ferrous and nickelous metals, such as iron, steel,nickel, nickel alloys and the like. In such cases, a tightly adherent orfirmly bonded coat of metal sulfide, iron sulfide or nickel sulfide asthe case may be, is formed on the surface of the metal by reaction ofthe metal with the hydrogen sulfide and oxygen. Iron, mild and lowalloyed steels react with hydrogen sulfide easily and extensively in thepresence of oxygen and water vapor at normal temperatures, i.e.,atmospheric or room temperatures. Some metals such as stainless steelsmay preferably require the use of a moderately elevated orsuperatmospheric temperature, for example, 50-80 C. A temperature withinthe range of about 80 C. will serve ordinarily for economic operationwith these and other ferrous metals such as high alloyed steels.

When proceeding according to my invention, by contacting a metal of theferrous group in the dry state with a hydrogen sulfide, oxygen and watervapor, a tightly adherent coating is formed which is very advantageousin the plastic deformation of the metal. The process is very simple andreliable, and it is economically carried out with but very smallmaterial and equipment requirements.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above process andin the article set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What I claim is:

1. A process for facilitating the plastic deformation of a metal articleof the ferrous group comprising the steps of producing a tightlyadherent sulfide coating on said article by contacting it, in theabsence of visible water on said article and in the presence of watervapor with stoichiometric amounts of hydrogen sulfide and oxygenaccording to the equation where R is a material selected from the groupconsisting of iron, nickel and cobalt, until a black coating of metalsulfide has been formed thereon and thereafter plastically deformingsaid coated metal article.

2. The process of claim 1 further defined in that said metal of theferrous group is an iron alloy.

3. The process of claim 1 further defined in that said hydrogen sulfideis free hydrogen sulfide.

4. The process of claim 1 further defined in that said hydrogen sulfideis provided by the volatilization of ammonium hydrosulfide.

5. A process for facilitating the plastic deformation of a metal articleof the ferrous group comprising the steps of producing a tightlyadherent sulfide coating on said article by coating it with an aqueoussolution of ammonium sulfide, drying said solution coating on' saidarticle in the open air, continuing to contact the resulting coatedarticle in air for about 20 to about minutes in the absence of visiblewater on said article until a black coating has formed according to theequation where R is a material selected from the group consisting ofiron, nickel and cobalt, and plastically deforming the sulfide coatedarticle.

6. The process of claim 5 further defined in that said ammonium sulfideis ammonium sulfide of the formula Q2 7. The process of claim 5 furtherdefined in that said ammonium sulfide is ammonium hydrosulfide.

8. The process of claim 5 further defined in that said ammonium sulfideis ammonium polysulfide.

9. The process of claim 5. further defined in that said ammonium sulfidesolution contains a thickening agent to increase its viscosity.

10. A ferrous metal article treated for plastic deformation, saidarticle being provided with a tightly adherent sulfide coating bycontacting it, in the absence of visible water on said article and inthe presence of water vapor with approximately stoichiometric amounts ofhydrogen sulfide and oxygen according to the equation R+H S+V2O RS+H O,where R is a material selected from the group consisting of iron,nickel, and cobalt.

11. A ferrous metal article of the class described having formed thereona tightly adherent sulfide coating by contacting it, in the absence ofvisible Water on said article and in the presence of water vapor withapproximately stoichiometric amounts of hydrogen sulfide and oxygenaccording to the equation R+H S+ /zO- RS+H O where R is a materialselected from the group consisting of iron, nickel and cobalt.

References Cited in the file of this patent UNITED STATES PATENTS2,054,737 Brunner Sept. 15, 1936 2,245,561 Nelson et al June 17, 19412,350,491 Butler et al. June 6, 1944 2,445,962 Mell July 27, 1948FOREIGN PATENTS 510,780 Belgium May 15, 1952

1. A PROCESS FOR FACILITING THE PLASTIC DEFORMATION OF A METAL ARTICLEOF THE FERROUS GROUP COMPRISING THE STEPS OF PRODUCING A TIGHTLYADHERENT SULFIDE COATING ON SAID ARTICLE BY CONTACTING IT, IN THEABSENCE OF VISIBLE WATER ON SAID ARTICLE AND IN THE PRESENT OF WATERVAPOR WITH STOICHIOMETIC AMOUNTS OF HYDROGEN SULFIDE AND OXYGENACCORDING TO THE EQUATION